Diesel/Electric Propulsion System Design - Have your say!

Discussion in 'Hybrid' started by CatBuilder, Sep 11, 2011.

  1. CatBuilder

    CatBuilder Previous Member

    Never thought I'd be going down this path, but it has come to light that given my charter house loads, I may be able to attain more efficiency using diesel/electric than I could using all the various traditional methods of propelling my catamaran.

    I started this thread with the hopes that some folks would weigh in here and help me understand some basics and where to source things.

    Here are my basic requirements:

    • 30HP (20kw?) thrust for each hull
    • Pod type electric motors (one for each hull) running from a main battery bank
    • 60HP?? 45KW?? DC Generator to charge battery bank and provide for house loads.
    • Some appropriate type of battery to store power - a lot of power. Lots of cycles and quick charging. Ideas?
    • Throttle/controller for drives, similar to Morse controls.
    • Large inverter to support electric oven and/or electric heat and air conditioning house loads.
    • Automatic control system to kick on the generator when the batteries get low and/or when the main drive motors are engaged.

    Jump right in if you can... and tell me where I'm wrong with the sizing of the generator, what weights these various components have, ideas you have for making the system run well, etc...

  2. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    Get Nigel Calders Boatowner's Mechanical and Electrical Manual. It has a lot of information about this specific subject.
    For me (for serious charter busines).. dual AC generators like Fisher-Panda, other one to cover the hotel load +some and the other one cover the thrust load - something like 15kW and 35kW, inverters to load the battery bank and for DC..
    Not too big battery bank (it's catamaran..) , a bit more than overnight hotel loads maybe..
  3. CatBuilder

    CatBuilder Previous Member

    Thanks, Teddy.

    Looking at the following YouTube video, I think I've already made one bad assumption:


    I am assuming I need a 30HP (20KW) electric motor to replace the 30HP (20KW) diesel engine the design calls for.

    In the YouTube video, they have a similar size catamaran and are using 10HP electric AC motors with a pair of Phasor 240VAC gensets, which are 12KW in power (20% safety factor over their AC electric motor ratings).

    I think I'm most of the way there on this stuff, since systems are my forte when it comes to boats. I just have little experience with knowing:

    1) How many HP electric is used for a given HP diesel engine?
    2) Are DC or AC motors best? I understand the modern AC motors have great controllers that give the AC motors the nice speed control from 0RPM to 1200RPM with full torque.
    3) What are state of the art (but kind of affordable) batteries for this type of system?

    Teddy: is your suggestion for dual generators a redundancy suggestion? I was thinking of possibly having the battery bank sized as a "get home" solution for a single hour of motoring with no generator in an emergency. She is a performance sailing vessel, so between sails, a single generator and a sizable battery bank, I figured that's enough redundancy. When all else fails, I have an anchor too. :)
  4. keysdisease
    Joined: Mar 2006
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    keysdisease Senior Member

    I don't believe the technology is yet ready for hybrid power on a boat your size to be viable.

    I have seen some hybrid boats (80 Mochi, got to crawl all over the engine room, cool) http://www.luxist.com/2008/10/05/ferrettis-new-hybrid-yacht-the-mochi-craft-long-range-23/
    and looked very closely at the systems at the Shows (IBEX, mastervolt, steyr) and I have a local customer I'm working with.

    I am very curious about this emerging technology and I follow it closely.

    The systems I've seen are complex, which is something I try and avoid. I like KISS.

    As others have indicated, there are probably a range of vessels doing specific jobs in a very routine fashion where the current technology makes sense. On a performance sailing catamaran, I think not yet.


  5. CatBuilder

    CatBuilder Previous Member

    Steve, I know you are one experienced mariner and we tend to agree on everything. I have a few "must haves" on my list that have been impossible to solve:

    1) High house loads for heat and air conditioning at anchor
    2) Retractible drive gear (no junk down there when I'm sailing)
    3) Keep weight as low as possible (keep boat on a diet)

    If you can find me a standard solution that meets #2, I'll install it. :D

    I was onto outboards for a while, but they aren't going to work. Either they are outside and exposed, or they are inside and overheat. Pick your poison.

    Definitely read my post a little more closely though. I'm not looking for any new technology or any hybrid system here. I'm looking to put together a diesel/electric system made from off the shelf, existing electric components and a generator. Something sort of like that YouTube video above, but tailored to my own specific needs. Nothing fancy or marketed to the marine industry. Generator, battery bank, electric drive motors and controllers. Nothing fancy or high tech.
  6. pool
    Joined: Sep 2010
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    pool Junior Member

    did you look at the Amartech retractable drive? should be straightforward to bolt an electric motor to its inboard cv joint, I think
  7. CatBuilder

    CatBuilder Previous Member

    Wow, cool! The Amartech solution is the closest I've seen to what I'm looking for, but I don't have enough room aft to install one. Between the engine and kick up rudders, there isn't enough space back there for a shaft to swing up as shown on the website. Great idea for someone else with the room, though.
  8. DGreenwood
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    DGreenwood Senior Member

    The Amartech system is VERY complex and suitable only for race boats or cruisers with unlimited funds.
  9. DGreenwood
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    DGreenwood Senior Member

  10. CatBuilder

    CatBuilder Previous Member

    Thanks, DGreenwood. I'm sort of familiar with those systems. I wonder though... can they be done without those terrible boxes added that reduce bridgedeck clearance?


    I'm doing a custom build right now, so the world is my oyster. I can put in anything that works. I was leaning toward off the shelf electrical components, like the YouTube video above details.

    Does Gideon own Green Motion as well as FastCat? I can't remember if he owns both. I'll give him a shout about seeing if Green Motion can be done without those bridge deck lowering boxes. Thanks for the reminder on that one.
  11. Bruce Woods
    Joined: Sep 2007
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    Bruce Woods Senior Member

    Ask your Designer.

    You've bought a set of plans from this guy, so I suspect you value his opinion.
    If the designer says 30 hp diesels are best for this application, then there's no discussion. I'm sure Richard Woods would also state his preferences if asked.
    There's a lot of race boats doing the Sydney Hobart each year with Diesels and sail-drives or shafts, that are a lot quicker than your cruiser. Go figure.
    Remember its a charter boat with 12 mm ply non structural bulkheads. Hardly high tech.
    Hope this helps.
  12. TeddyDiver
    Joined: Dec 2007
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    TeddyDiver Gollywobbler

    It's bcs the hotel loads and thrust loads are so different. Smaller gen set runs during day time, covers the hotel loads, loads the batteries up for the next night and you have some reserve to run the engines occasionally (not full spedd of course). Long legs with engine power with the bigger gen set.
    This way you get the best loading for both gensets and redundancy too..
    What comes to combustion vs electric kW.. it's just that an electric motor you can run continiously 100% but combustion is recommended for around 70% of full throtle..
    BR Teddy
  13. masalai
    Joined: Oct 2007
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    masalai masalai

    The Harmony setup seems well researched but I feel, when motoring, the speed will be S.L.O.W. I have twin nanni/kubota 21hp (15.4KW) saildrives that have, (with 2 blade 15 x 10 pitch folding propellers), given 8 knots and I probably had a bit of tidal assist there...

    I am about to fit fixed, 3 blade 15 x 11, and I hope to do better... see http://www.boatdesign.net/forums/boat-building/my-little-piece-peace-25962-113.html#post486084 and go back for images of most of the build...
    Joined: Oct 2002
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    FAST FRED Senior Member

    If ca$h , reliability and maint is of a concern I think an OTS diesel setup , but with HUGE time and effort spend on soundproofing and isolating the package would be my choice.

    For an extra $50K or $100K you could quadruple the complexity ,decrease the efficiency but sell "Green" to folks, the repairs and efficiency cost could come out of the advertising budget.

  15. CatBuilder

    CatBuilder Previous Member

    Bruce, I realize I haven't posted many pictures or facts about my build. Sorry about that. You are missing a lot about it. It's a very fast catamaran make completely of Corecell using a modified Tornado hull designed by Kurt Hughes. It's as near to a racing cat as you can cruise safely with (IMO). There are a grand total of 5 of these "ultra heavy" 12mm Okoume ply bulkheads in each hull. The cross beam bulkheads are all Corecell/glass. The grand total different between making these 5 bulkheads per hull from Corecell vs. the Okoume is approximately 100lbs. The weight of my wife. I think I can make that 100lbs up elsewhere, possibly by doing diesel/electric. :D

    Here is what these Okoume bulkheads look like. Do they look heavy?


    My designer doesn't care how you power the boat. The plans have instructions for inboard diesels or outboards or whatever you want. It's a sailing machine with auxiliary propulsion, not a motorsailer, so it really doesn't matter what I do, as long as I can motor consistently in various conditions.

    Hope that clears up the kind of boat this is.

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